1. Field of the Invention
The present invention relates to a projection-type-display device which can be applied to for example a projector device for projecting an optical image spatially modulated by a reflection-type liquid crystal panel onto a screen.
2. Description of the Related Art
In the related art, a projection-type display device has been proposed which is configured to use a reflection-type liquid crystal panel to generate a spatially modulated optical image and to project this optical image onto the screen so as to form a desired color image.
FIG. 1 is a view of the configuration of this type of projection-type display device.
In this projection-type display device 1, a light source 2 is constituted by for example a discharge lamp 3 and a reflector 4 and emits white illumination light. A convex lens 5 converts the illumination light emitted from the light source 2 to a substantially parallel luminous flux and then emits it.
A color separation mirror 6 on the optical path of the illumination light emitted from this convex lens 5 reflects the illumination light having a predetermined wavelength and transmits the remaining illumination light therethrough. A color separation mirror 7 on the optical path of the illumination light reflected at this color separation mirror 6 reflects the illumination light having a predetermined wavelength and transmits the remaining illumination light therethrough. Due to this, the projection-type display device 1 separates the illumination light emitted from the light source 2 to red, blue, and green illumination light.
A lens 8, a mirror 9, and a lens 10 bend the optical path of the illumination light transmitted through the color separation mirror 6 to guide the light to a polarization beam splitter 11. The polarization beam splitter 11 emits illumination light having a predetermined plane polarization in the illumination light striking from this lens 10 toward a reflection-type liquid crystal panel 12 and transmits the illumination light having a plane polarization orthogonal to this plane polarization. Further, the polarization beam splitter 11 transmits a predetermined polarization component in the optical image emitted after spatially modulating the illumination light at the reflection-type liquid crystal panel 12 and emits it to a color synthesizing prism 13.
A polarization beam splitter 14 similarly emits the illumination light having a predetermined plane polarization in the illumination light reflected at the color separation mirror 7 toward the reflection-type liquid crystal panel 15 and transmits the illumination light having the plane polarization orthogonal to this plane polarization therethrough. Further, the polarization beam splitter 14 transmits a predetermined polarization component in the optical image emitted after spatially modulation of the illumination light at the reflection-type liquid crystal panel 15 therethrough and emits it to the color synthesizing prism 13.
A polarization beam splitter 16 similarly emits the illumination light having a predetermined plane polarization in the illumination light reflected at the color separation mirror 7 toward the reflection-type liquid crystal panel 17 and transmits the illumination light having a plane polarization orthogonal to this plane polarization therethrough. Further, the polarization beam splitter 16 transmits a predetermined polarization component in the optical image emitted after spatially modulation of the illumination light at the reflection-type liquid crystal panel 17 therethrough and emits it to the color synthesizing prism 13.
The reflection-type liquid crystal panels 12, 15, and 17 spatially modulate the illumination light according to color signals corresponding to the wavelengths of the incident illumination light by being driven by a not illustrated drive circuit and project optical images rotated in their plane polarizations with respect to the illumination light toward the polarization beam splitters 11, 14, and 16.
The color synthesizing prism 13 combines the optical images incident from these polarization beam splitters 11, 14, and 16 and emits the result. A projection lens 19 projects the resultant optical image emitted from this color synthesizing prism 13 onto the screen 20.
Due to this, the projection-type display device 1 enlarges and projects the images formed on the reflection-type liquid crystal panels 12, 15, and 17 onto the screen 20 to thus display the intended color image.
The polarization beam splitters 11, 14, and 16 used for this type of projection-type display device 1, however, also reflect and emit several percent of the amount of light incident of the components of plane polarization which originally must be transmitted. In the projection-type display device 1, therefore, the unrequired plane polarization components reflected at the polarization beam splitters 11, 14, and 16 in this way are returned from the reflection-type liquid crystal panels 12, 15, and 17 to the polarization beam splitters 11, 14, and 16 and projected onto the screen 20 via the color synthesizing prism 13.
Further, unmodulated components which are never polarized, but are reflected are also contained also in the modulated light reflected at the reflection-type liquid crystal panels 12, 15, and 17. In the projection-type display device 1, such components are also projected onto the screen 20 via the color synthesizing prism 13.
Due to this, the projection-type display device 1 suffers from the defect of the haze phenomenon where a portion which should be originally displayed black is displayed white, so there is a problem that the contrast of the display image is still insufficient by that amount in practical use and the quality of the display image is poor.
Below, this haze phenomenon will be further considered from the viewpoint of the structure of the polarization beam splitter.
When a black portion is displayed white and this haze phenomenon is manifested, the contrast cannot be sufficiently secured by that amount in the image displayed on the screen.
A polarization beam splitter is formed by adhering inclined facets of rectangular prisms to each other. The incident light is detected by a laminate of dielectric films at the inclined facets. Accordingly, in the transmitted light and the reflected light of the polarization beam splitter, originally the linear polarized light resulting from this detection must be emitted.
The glass material constituting this type of rectangular prism, however, has a birefringence property. Due to this, the reflected light and the transmitted light to be originally emitted by the linear polarization are emitted by elliptical polarization.
Namely, the reflected light and the transmitted light comes to contain light having a plane polarization orthogonal to the plane polarization originally aimed at. Further, the light incident due to linear polarization comes to be detected by elliptical polarization, therefore part of the light to be originally transmitted or reflected will be reflected or transmitted by that amount and emitted reverse to the former.
When viewing this from the standpoint of the optical images emitted toward the polarization beam splitters from the reflection-type liquid crystal panels, the reflection-type liquid crystal panels spatially modulate the incident light having the predetermined plane polarizations and reflect optical images as the synthesized light of p-polarization components and s-polarization components. The optical images emitted in this way originally must be separated into the p-polarization components and the s-polarization components by the polarization beam splitters and only the optical images of the p-polarization components projected onto the screen.
However, the optical images become elliptical polarized light due to the birefringence of the polarization beam splitters. As a result, part of the s-polarization components subjected to no spatial modulation will be projected onto the screen.
Further, when viewing the illumination light emitted from the polarization beam splitters toward the reflection-type liquid crystal panels, the components of the plane polarization orthogonal to the illumination light having the predetermined plane polarization to be spatially modulated at the reflection-type liquid crystal panels will leak in. This leaked illumination light will be projected onto the screen as it is.
Note that, if the above haze phenomenon nonuniformly occurs, the image displayed in the projection-type display device 1 will deteriorate in uniformity.
An object of the present invention is to provide a projection-type display device capable of displaying a high quality display image by improving the contrast.
According to a first aspect of the present invention, there is provided a projection-type display device, comprising at least a first reflection-type image-forming means for spatially modulating and reflecting an incident first illumination light to emit a first optical image, a second reflection-type image-forming means for spatially modulating and reflecting an incident second illumination light to emit a second optical image, a wavelength separation mirror for reflecting illumination light of a predetermined wavelength in incident light and emitting it as the first illumination light to the first reflection-type image-forming means and transmitting the remaining illumination light and emitting it as the second illumination light to the second reflection-type image-forming means so as to reflect the first optical image and transmit the second optical image and emit the first and second optical images so as to follow the optical path of the incident light in reverse, a projection optical system for projecting the first and second optical images, a light source for emitting predetermined light to the wavelength separation mirror as the incident light, and a light separating means for emitting the incident light emitted from the light source to the wavelength separation mirror and emitting the first and second optical images incident from the wavelength separation mirror to the projection optical image, the inclination of the wavelength separation mirror set so that the optical axis of the light incident on the wavelength separation mirror and the optical axis of the first optical image becomes smaller than 90 degrees.
According to a second aspect of the present invention, there is provided a projection-type display device, comprising at least a first reflection-type image-forming means for spatially modulating and reflecting an incident first illumination light to emit a first optical image, a second reflection-type image-forming means for spatially modulating and reflecting an incident second illumination light to emit a second optical image, a third reflection-type image-forming means for spatially modulating and reflecting an incident third illumination light to emit a third optical image, a first wavelength separation mirror for reflecting illumination light of a predetermined wavelength in incident light and emitting it as the first illumination light to the first reflection-type image-forming means and transmitting and emitting the remaining illumination light so as to reflect the first optical image and transmit the second and third optical images and emit the first, second, and third optical images so as to follow the optical path of the incident light in reverse, a second wavelength separation mirror for reflecting illumination light of a predetermined wavelength in light transmitted through the first wavelength separation mirror and emitting it as the second illumination light to the second reflection-type image-forming means and transmitting the remaining illumination light and emitting it as the third illumination light to the third reflection-type image-forming means so as to reflect the second optical image and transmit the third optical image and emit the second and third optical images toward the first wavelength separation mirror, a projection optical system for projecting the first, second, and third optical images, a light source for emitting predetermined light to the first wavelength separation mirror as the incident light, and a light separating means for emitting the incident light emitted from the light source to the first wavelength separation mirror and emitting the first, second, and third optical images incident from the first wavelength separation mirror to the projection optical image, the inclination of the first wavelength separation mirror set so that the optical axis of the light incident on the first wavelength separation mirror and the optical axis of the first optical image becomes smaller than 90 degrees, the inclination of the second wavelength separation mirror set so that the optical axis of the light incident on the second wavelength separation mirror and passing through the first wavelength separation mirror and the optical axis of the second optical image becomes smaller than 90 degrees.
Preferably, the first reflection-type image-forming means emits the first optical image with a plane polarization rotated with respect to the incident light and a polarization filter for selectively transmitting illumination light of a plane polarization corresponding to the plane polarization of the light incident on the first reflection-type image-forming means is arranged between the light source and the light separating means.
Alternatively, preferably, the first reflection-type image-forming means emits the first optical image with a plane polarization rotated with respect to the incident light and a polarization filter for selectively transmitting incident light of a plane polarization corresponding to the plane polarization of the first optical image is arranged between the projection optical system and the light separating means.
Alternatively, preferably, the first reflection-type image-forming means emits the first optical image with a plane polarization rotated with respect to the incident light, a first polarization filter for selectively transmitting illumination light of a plane polarization corresponding to the plane polarization of the light incident on the first reflection-type image-forming means is arranged between the light source and the light separating means, and a second polarization filter for selectively transmitting incident light of a plane polarization corresponding to the plane polarization of the first optical image is arranged between the projection optical system and the light separating means.
According to a third aspect of the present invention, there is provided a projection-type display device, comprising a reflection-type image-forming means for spatially modulating and reflecting illumination light of a predetermined plane polarization to emit an optical image with a plane polarization rotated with respect to the plane polarization of the illumination light, a projection optical system for projecting the optical image, a light source for emitting the illumination light, and a light separating means for emitting the illumination light emitted from the light source toward the reflection-type image-forming means and emitting the optical image emitted from the reflection-type image-forming means to the projection optical system, a polarization separation element for selectively transmitting illumination light of a plane polarization corresponding to the plane polarization of the light incident on the reflection-type image-forming means and selectively reflecting the component of the plane polarization orthogonal to that plane polarization arranged between the light source and the light separating means.
Preferably, the polarization separation element is formed on an incident facet of the illumination light of the light separating means.
According to a fourth aspect of the present invention, there is provided a projection-type display device provided with a reflection-type image-forming means for spatially modulating and reflecting illumination light of a predetermined plane polarization to emit an optical image with a plane polarization rotated with respect to the plane polarization of the illumination light, a projection optical system for projecting the optical image, a light source for emitting the illumination light, and a light separating means for emitting the illumination light emitted from the light source toward the reflection-type image-forming means and emitting the optical image emitted from the reflection-type image-forming means to the projection optical system, a polarization separation element for selectively transmitting incident light of a predetermined plane polarization corresponding to the plane polarization of the optical image and selectively reflecting the component of the plane polarization orthogonal to that plane polarization arranged between the projection optical system and the light separating means.
Preferably, the polarization separation element is formed on an emission facet of the optical image of the light separating means.
According to a fifth aspect of the present invention, there is provided a projection-type display device provided with a reflection-type image-forming means for spatially modulating and reflecting illumination light of a predetermined plane polarization to emit an optical image with a plane polarization rotated with respect to the plane polarization of the illumination light, a projection optical system for projecting the optical image, a light source for emitting the illumination light, and a light separating means for emitting the illumination light emitted from the light source toward the reflection-type image-forming means and emitting the optical image emitted from the reflection-type image-forming means to the projection optical system, a first polarization separation element for selectively transmitting illumination light of a plane polarization corresponding to the plane polarization of the light incident on the reflection-type image-forming means and selectively reflecting the component of the plane polarization orthogonal to that plane polarization arranged between the light source and the light separating means, a second polarization separation element for selectively transmitting incident light of a predetermined plane polarization corresponding to the plane polarization of the optical image and selectively reflecting the component of the plane polarization orthogonal to that plane polarization arranged between the projection optical system and the light separating means.
Preferably, the first polarization separation element is formed on an incident facet of the illumination light of the light separating means.
Alternatively, preferably the second polarization separation element is formed on an emission facet of the optical image of the light separating means.
According to a sixth aspect of the present invention, there is provided a projection-type display device provided with a reflection-type image-forming means for spatially modulating illumination light of a predetermined plane polarization to emit an optical image with a plane polarization rotated with respect to the plane polarization of the illumination light, a projection optical system for projecting the optical image, a light source for emitting the illumination light, and a polarization beam splitter for emitting the illumination light emitted from the light source toward the reflection-type image-forming means and emitting a predetermined polarization component in the optical light incident from the reflection-type image-forming means to the projection optical system, the polarization beam splitter being formed by a member satisfying the following relationship:       5.00    xc3x97          10      2        ≥            K      ·      α      ·      E      ·              Cp        ρ              ⁢                  ∫                  λ          2                          λ          1                    ⁢                        (                      1            -            T                    )                ⁢                  ⅆ          λ                    
where,
K: photoelasticity constant of the member (nm/mmxc2x7mm2/N),
xcex1: linear expansion coefficient of the member (10xe2x88x926/K),
E: Young""s modulus of the member (103N/mm2),
xcex: wavelength of the illumination light (nm),
T: internal transmittance of the member at the wavelength xcex,
xcfx81: specific gravity of the member (g/cm3), and
Cp: specific heat of the member (J/gxc2x7k),
the integration range in Equation being a range of the light absorption wavelength band of the member.
According to a seventh aspect of the present invention, there is provided a projection-type display device provided with a plurality of reflection-type image-forming means each of which for spatially modulating incident light of a predetermined wavelength and emitting an optical image with a plane polarization rotated with respect to the plane polarization of the incident light, a light source for emitting illumination light, a dichroic prism for emitting illumination light emitted from the light source to the plurality of reflection-type image-forming means based on wavelength and emitting the optical images incident from the plurality of reflection-type image-forming means so as to run in reverse along the optical axis of the illumination light, a projection optical system for projecting the optical images, and a polarization beam splitter for emitting the illumination light emitted from the light source toward the dichroic prism and emitting a predetermined polarization component in the optical images incident from the dichroic prism to the projection optical system, the polarization beam splitter and/or the dichroic prism being formed by a member satisfying the following relationship:       5.00    xc3x97          10      2        ≥            K      ·      α      ·      E      ·              Cp        ρ              ⁢                  ∫                  λ          2                          λ          1                    ⁢                        (                      1            -            T                    )                ⁢                  ⅆ          λ                    
where,
K: photoelasticity constant of the member (nm/mmxc2x7mm2/N),
xcex1: linear expansion coefficient of the member (10xe2x88x926/K),
E: Young""s modulus of the member (103N/mm2),
xcex: wavelength of the illumination light (nm),
T: internal transmittance of the member at the wavelength xcex,
xcfx81: specific gravity of the member (g/cm3), and
Cp: specific heat of the member (J/gxc2x7k),
the integration range in Equation being a range of the light absorption wavelength band of the member.
Preferably, the light absorption wavelength band is a range of 420 nm to 500 nm.
Alternatively, preferably, a polarization separation element for selectively transmitting illumination light of a plane polarization corresponding to the plane polarization of the light incident on the reflection-type image-forming means and selectively reflecting the component of the plane polarization orthogonal to that plane polarization is arranged between the light source and the polarization beam splitter.
Preferably, the polarization separation element is formed on an incident facet of the illumination light of the polarization beam splitter.
Alternatively, preferably, a polarization separation element for selectively transmitting incident light of a predetermined plane polarization corresponding to the plane polarization of the optical image and selectively reflecting the component of the plane polarization orthogonal to that plane polarization is arranged between the projection optical system and the polarization beam splitter.
Preferably, the polarization separation element is formed on an emission facet of the optical image of the polarization beam splitter.
According to the present invention, if the inclination of the wavelength separation mirror is set so that the angle exhibited by the optical axis of the incident light on the wavelength separation mirror and the optical axis of the first optical image becomes smaller than 90 degrees, it is possible to reduce the difference of the wavelengths in the p-polarization component and the s-polarization component reflected at the wavelength separation mirror. Accordingly, a high quality image can be displayed by improving the efficiency of utilization of the illumination light by that amount.
Further, if the inclination of the first wavelength separation mirror is set so that the angle exhibited by the optical axis of the incident light on the first wavelength separation mirror and the optical axis of the first optical image becomes smaller than 90 degrees and, further, if the inclination of the second wavelength separation mirror is set so that the angle exhibited by the optical axis of the light incident on the second wavelength separation mirror and transmitted through the first wavelength separation mirror and the optical axis of the second optical image becomes smaller than 90 degrees, the difference of wavelengths in the p-polarization component and the s-polarization component of the reflected light can be reduced in wavelength separation mirrors having a so-called three-plate type structure and, accordingly, a high quality image can be displayed by improving the efficiency of utilization of the illumination light by that amount.
If a polarization separation element is arranged between the light source and the light separating means, the component never modulated by the reflection-type image forming means is blocked and this component can be returned to the light source side. By this, a lowering of the contrast due to the projection of this component is prevented, and thus the high quality image can be displayed. Further, the efficiency of utilization of the illumination light can be improved by utilizing this component again, and a temperature rise can be prevented by that amount.
Further, if a polarization separation element is arranged between the projection optical system and the light separating means, the component lowering the contrast in the projected image is blocked and this component can be returned to the light source side. By this, the lowering of the contrast due to the projection of this component is prevented and a high quality image can be displayed. Further, the efficiency of utilization of the illumination light can be improved by utilizing this component again, and a temperature rise can be prevented by that amount.
Further, according to the present invention, even if the birefringence is increased in a member satisfying the relationships due to an increase of stress by the rise of the temperature, the degree of the birefringence can be made to stay in a range enough for the practical use. By this, the above haze phenomenon due to the birefringence can be reduced and it becomes possible to improve the contrast by that amount and display a high quality display image.